武汉地区ZK145钻孔沉积物磁性特征及对古洪水的记录

Magnetic Characteristics of ZK145 Borehole Sediments in Wuhan Area and Its

长江中游是我国洪灾最为严重的地区,武汉江段是长江中游防洪重点.开展武汉地区长江古洪水研究,从而延长古洪水记录具有重要意义.选择长江武汉段堤后典型湖泊钻孔——ZK145钻孔,在沉积物岩性及沉积相分析的基础上,通过对岩心磁性特征和粒度特征分析,结合AMS14C测年,对长江武汉段全新世古洪水频发期进行了研究.根据质量磁化率、频率磁化率曲线,将钻孔划分为5个沉积阶段.再结合中值粒径和砂含量,识别出9次特大古洪水事件,其年代为:10580~10510,10280~10200,9690~9670,9530~9500,8660~8450,7700~7500,6270~5910,4850~4800,3560~3500 cal.a BP,其中9700~4800 cal.a.BP为古洪水频发期.热磁曲线分析表明,古洪水沉积物的热磁曲线在510℃附近可见较明显的峰值,主导磁性矿物为磁铁矿.研究表明,质量磁化率高值、频率磁化率低值和较粗粒径为长江武汉段堤后湖泊古洪水沉积的识别标志.

The middle reaches of the Yangtze River are the most severely affected areas in China,and the Wuhan section is the key to flood control in the middle reaches of Yangtze River.It is of great significance to study the paleoflood of the Yangtze River in Wuhan area so as to prolong the record of the paleoflood.In this study,ZK145 borehole was selected in a typical lake behind the dam of Wuhan section of the Yangtze River.Based on the analysis of sedimentary lithology and sedimentary facies,magnetic characteristics and particle size characteristics of the core were analyzed,and AMS14 C dating was used to study the occurrence period of holocene paleoflood in wuhan section of the Yangtze River.The borehole is divided into five sedimentary stages based on the mass magnetic susceptibility(χ)and the frequency susceptibility(χfd%)curve.Combined with the median particle size and sand content,nine paleoflood events were identified,with the age:10580-10510,10280-10200,9690-9670,9530-9500,8660-8450,7700-7500,6270-5910,4850-4800,3560-3500 cal.a BP,paleofloods occurred frequently at 9700-4800 cal.a BP among them.Through analysis of temperature-dependent magnetic susceptibility(κ-T curve),the heating curve of the paleoflood sediments shows a more obvious peak near 510℃in paleoflood sediments,and Magnetite is the dominant magnetic mineral.The research shows that the high mass magnetic susceptibility,the low frequency susceptibility and the coarser particle size are the identification marks of the paleoflood deposition in the lakes behind the Yangtze River embankment in the Yangtze River.